More vRAM means the GPU can hold and ultimately render more complex images and textures on the graphics chip, resulting in faster performance.

Is it bad to increase your VRAM?

Nothing. You can only allocate RAM to integrated graphics so this won't do anything for your dedicated GT740. So essentially I can increase the vram with no harm.

Is it bad to use 100% VRAM?

Given game needs (and uses) only certain amount of vram at given resolution/settings. If that amount is less then GPU's vram that's ok. If that amount is higher then GPU'd vram then you run into trouble - namely lots of stuttering. Simply put, as long as it is below 100% there is nothing to worry.